Question
How does a switchmode voltage regulator work?
Answer Options
- A) By alternating the output between positive and negative voltages
- B) By varying the duty cycle of pulses input to a filter
- C) By varying the conductivity of a pass element
- D) By switching between two Zener diode reference voltages
Correct Answer: B
Explanation
A switchmode voltage regulator (SMPS - Switch-Mode Power Supply) differs significantly from a linear regulator in that it does not use a continuous analog pass transistor to dissipate excess voltage as heat. Instead, it operates digitally for high efficiency.
A switchmode regulator works by varying the duty cycle of pulses input to a filter (inductor/capacitor network). The input voltage is rapidly switched on and off, and the ratio of ‘on’ time to total time (the duty cycle) is precisely controlled by a feedback loop to generate the desired average DC output voltage after the filtering stage. Since the control element acts as a low-loss switch, this architecture achieves efficiencies often greater than 90\%, making it much cooler and smaller than an equivalent linear supply.
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